Solar powered thermal distillation with zero liquid discharge

ABSTRACT

A solar powered thermal distillation system and method includes a solar still having a first end and an opposite second end with a longitudinal access extending between the first end and the opposite second end, the solar still further having a raised side and an opposite lowered side with a width axis extending between the raised side and the opposite lowered side. A solar-transmitting roof is located atop the solar still, wherein the solar-transmitting roof admits solar energy to equipment maintained within the solar still. The solar sill also includes a heating surface inclined along a direction aligned with or parallel to the width axis so that water flows down the heating surface along or parallel with the width axis, and a tubular member extending below the heating surface between the raised side and the opposite lowered side.

CROSS-REFERENCE TO PROVISIONAL APPLICATION

This nonprovisional patent application claims the benefit under 35U.S.C. §119(e) and priority to U.S. Provisional Patent Application Ser.No. 62/267,415 filed on Dec. 15, 2015, entitled “Solar Powered ThermalDistillation With Zero Liquid Discharge,” which is hereby incorporatedherein by reference in its entirety.

TECHNICAL FIELD

Embodiments are related to the field of solar powered thermaldistillation. Embodiments also relate to the use of multi-stage ormulti-effect thermal distillation (such as, but not limited to,multi-stage flash, membrane distillation, multi-effect distillation, orvapor (re)compression) with solar as the energy source producing onlypure water and dry salt from salty and saline source water. Embodimentsfurther relate to a process for desalination, and more specifically, toa process for desalination involving a solar distillation still having aheating surface orientation designed to maximize solar energy captureand multiple modules of thermal distillation thereby enhance the yieldof potable water in a desalination process.

BACKGROUND

The global population is growing and its resource dependency is growingaccordingly. More so, impoverished countries around the world havelimited means to provide food and water to its inhabitants. The worldhas an abundance of water, however, only three percent of it isconsidered clean enough to drink. There is thus a continuing need todevelop improved desalination technology, which could make use of theworld's vast brackish and saline water resources.

Desalination is a process that removes minerals from saline water.Desalination also can involve the removal of salts and minerals fromtarget substance such as in the case of soil desalination. During adesalination procedure, saltwater is desalinated to produce watersuitable for human consumption or irrigation. Due to its energyconsumption, desalinating sea water is generally more costly than usingfresh water from rivers or groundwater, water recycling, and waterconservation. However, these alternatives are not always available anddepletion of reserves is a critical problem worldwide. Desalination isparticularly relevant in dry areas such as in the American west,Australia, the Middle East, and Africa, to name a few areas, whichtraditionally have relied on collecting rainfall behind dams for water.

Solar distillation is a method of purifying water by harnessing thesun's energy. Solar distillation involves the use of solar energy toevaporate water and collect its condensate within the same closedsystem. Unlike other forms of water purification, solar distillation canconvert salt or brackish water into fresh drinking water. The structurethat houses the process is known as a solar still and although the size,dimensions, materials, and configuration are varied, all rely on aprocedure wherein an influent solution enters the system and the morevolatile solvents leave in the effluent leaving behind the salty solutebehind.

Solar distillation is thus an effective technique for purifyingseawater/brackish water because it can produce water as clean as, forexample, 10 mg/L of total dissolved solids (TDS). Solar stills, however,have not been widely employed because the classic still only producesapproximately 3 liters per day per square meter of solar capture. Thisposes a challenge since the amount of drinking water consumed per personis approximately 2 liters per day. Over time, other methods of waterfiltration have been developed. Reverse osmosis, for example, iscurrently the most popular method of desalinating water, but it isenergy intensive and subject to high operating costs, which renders itunreasonable for insolvent regions.

FIG. 1 illustrates a schematic diagram of the basic thermodynamicoperation of a prior art solar still. Solar distillation is analternative for desalinating and sanitizing water using solar energyfrom the sun. The functioning of solar still is shown in FIG. 1. The“classic” solar still can vary geometrically from semispherical shapesto pyramids. The solar still includes a trough 14 and a basin 15. Thetrough 14 is responsible for collecting condensate. A basic solardistiller functions with the basin 15 filled with water 16 that ismanually or automatically fed into the basin 15. The sunlight radiationstrikes the bottom of the basin 15 where the water 16 is standing, andsolar thermal energy heats the water 16 and increases vaporization.Arrows 10 shown in FIG. 1 indicates incoming solar energy.

As the water 16 evaporates, it leaves behind contaminants such as salt,bacteria, and other substances that compromise the water 16. Water vaporis shown in FIG. 1 as rising, as indicated by arrows 12. As the watervapor reaches the glass 13, heat escapes through the glass 13, leavingbehind water vapor with low kinetic energy. As the air becomes saturatedwith moisture, water molecules begin to condense on the glass surface,which forms water droplets that travel to the trough 14. The trough isan apparatus that collects the water droplets and empties it into acontainer such as a bottle. Water distillers can purify a wide varietyof water from brackish groundwater to seawater.

Attempts have thus been made to provide solar stills capable ofproducing relatively large quantities of potable water. These attemptshave proven to be costly and inefficient and have failed at producinglarge quantities of potable water. Other desalination technology iscomplex, energy intensive, and delivers only low yield from feed water.Therefore, a need exists for an improved solar collection systemcombined with thermal distillation.

BRIEF SUMMARY

The following summary is provided to facilitate an understanding of someof the innovative features unique to the disclosed embodiments and isnot intended to be a full description. A full appreciation of thevarious aspects of the embodiments disclosed herein can be gained bytaking the entire specification, claims, drawings, and abstract as awhole.

It is, therefore, one aspect of the disclosed embodiments to provide fora solar collection system and method combined with thermal distillation.

It is another aspect of the disclosed embodiments to provide for the useof multi-stage or multi-effect thermal distillation (such as, but notlimited to, multi-stage flash, membrane distillation, multi-effectdistillation, or vapor (re)compression) with solar as the energy sourceproducing only pure water and dry salt from salty and saline sourcewater.

It is yet another aspect of the disclosed embodiments to provide forimproved systems, devices, and methods for desalination.

It is a further aspect of the disclosed embodiments to provide forsystems, devices, and methods for desalination involving a solardistillation still (“solar still”) having a heating surface orientationconfigured to maximize solar energy capture and multiple modules ofthermal distillation, thereby enhancing the yield of potable water in adesalination process.

It is also an aspect of the disclosed embodiments to provide for athermal powered solar distillation method and system based on a cycledarrangement, such as with day and night cycles, to further enhance theyield of potable water.

The aforementioned aspects and other objectives and advantages can nowbe achieved as described herein. In accordance with one exampleembodiment, an innovative solar can be implemented, which outperformsthe production of the classic solar still. In such an exampleembodiment, a PVC return duct can be integrated into the system and/orapparatus to return cold air coming out of the top of the condenser tothe base of the inclined thin film within the solar collector. Thedesign of the cold air return duct provided natural, buoyancy-drivenconvection through the first effect to provide consistent and smooth airflow. This improvement results in more uniform and consistenttemperature performance in the solar collector and the condenser, butmost importantly, heat transfer through the wall of the duct allowswater to condense inside the duct. Implementation of this duct improvedthe water production of the system by 20-30%. The flow rate can bemodulated and controlled for efficient air flow through the system by atleast one integrated valve.

In another example embodiment, a novel countercurrent flow system can beintegrated into the solar system without an external PVC return duct.The disclosed advanced solar distillers have improved on the classicsolar still by at least a factor of, for example, 3.

A variety of example embodiments are disclosed herein. For example, inone embodiment, a solar powered thermal distillation system can beconfigured, which includes a solar still having a first end and anopposite second end with a longitudinal access extending between thefirst end and the opposite second end, the solar still further having araised side and an opposite lowered side with a width axis extendingbetween the raised side and the opposite lowered side and at least onesolar-transmitting roof atop the solar still, wherein the at least onesolar-transmitting roof admits solar energy to electrical and/orelectromechanical equipment maintained within the solar still. The solarstill can be configured to include a heating surface inclined along adirection aligned with or parallel to the width axis so that water flowsdown the heating surface along or parallel with the width axis. Thesolar still can further include a tubular member that extends below theheating surface between the raised side and the opposite lowered side.The solar still can also include one or more collection troughspositioned to receive condensed water dripping from the tubular member.

In another example embodiment, the aforementioned solar still caninclude a liquid distributor positioned along the raised side of theheating surface to distribute water discharged from the liquiddistributor substantially across a length of heating. In some exampleembodiments, the energy recovered in the solar still can be provided inthe form of heated water delivered to a vessel operated under a vacuum.

In some example embodiments, the aforementioned vessel can include thetubular member and the collection trough (or troughs) to collectcondensate dripping from the tubular member. In another exampleembodiment, the vessel can be enclosed within an exterior vessel that isalso maintained under a vacuum condition such that the vessel comprisesan interior vessel maintained within the exterior vessel. In someexample embodiments, water that does not flash can be transferred toanother vessel operated at a greater vacuum for further flashing.

In yet another example embodiment, the aforementioned interior andexterior vessels can be configured with a pair of internal and externalcontainment vessels in association with the tubular member and the atleast one collection trough to recover condensed water, wherein the pairof internal and external containment vessels constitute a onestage/effect and a multiple stages/effects, each with greater vacuum ortemperature, which are combinable to produce pure water at each of themultiple stages/effects.

Water heated in the multiple stages/effects can be used to condenseflashed water vapor in earlier and hotter stages and routed through thesolar still to a first stage. Additionally, cold water heated in thetubular member can be stored in the vessel, and the vessel can include(in some example embodiments) a transparent canopy with sloped roof. Thetransparent canopy can be configured with, for example, a plurality oftroughs for collecting purified water.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, in which like reference numerals refer toidentical or functionally-similar elements throughout the separate viewsand which are incorporated in and form a part of the specification,further illustrate the present invention and, together with the detaileddescription of the invention, serve to explain the principles of thepresent invention.

FIG. 1 illustrates a schematic diagram of the basic thermodynamicoperation of a prior art solar still;

FIG. 2 illustrates a three-dimensional view of a solar still apparatus,which can be implemented in accordance with a preferred embodiment;

FIG. 3 illustrates a sample image of a GUI (Graphical User Interface) inaccordance with an example embodiment;

FIG. 4 illustrates a schematic diagram of a system composed of anarrangement of thermocouples, humidity sensors, and conductivity cells,in accordance with an example embodiment;

FIG. 5 illustrates a pictorial diagram of a cold-air return duct, whichcan be implemented in accordance with an example embodiment;

FIG. 6 illustrates a water production comparison chart, in accordancewith an example embodiment;

FIG. 7 illustrates a solar collector air vent, in accordance with anexample embodiment;

FIG. 8 illustrates a graph depicting data indicative of heat lossthrough a double-pane glass, in accordance with an example embodiment;

FIG. 9 illustrates an image of an evaporator glass 150, which may beimplemented in accordance with an example embodiment;

FIG. 10 illustrates an image of a condenser coil 160, which can beimplemented in accordance with an example embodiment;

FIGS. 11A-11B illustrate graphs indicative of sample day-cycleperformance (April 4), in accordance with an example embodiment;

FIGS. 12-12B illustrate graphs indicative of sample day-cycleperformance (April 6), in accordance with an example embodiment;

FIGS. 13A-13B illustrate graphs indicative of sample day-cycleperformance (April 11), in accordance with an example embodiment;

FIGS. 14A-14B illustrate graphs indicative of sample day-cycleperformance (April 19), in accordance with an example embodiment;

FIGS. 15A-15B illustrate graphs indicative of sample day-cycleperformance (April 26), in accordance with an example embodiment;

FIGS. 16A-16B illustrate graphs indicative of sample day-cycleperformance (April 27), in accordance with an example embodiment; and

FIG. 17 illustrates a block diagram of a solar powered thermaldistillation system, in accordance with an example embodiment.

DETAILED DESCRIPTION

The particular values and configurations discussed in these non-limitingexamples can be varied and are cited merely to illustrate at least oneembodiment and are not intended to limit the scope thereof.

The embodiments will now be described more fully hereinafter withreference to the accompanying drawings, in which illustrativeembodiments of the invention are shown. The embodiments disclosed hereincan be embodied in many different forms and should not be construed aslimited to the embodiments set forth herein; rather, these embodimentsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the invention to those skilled in theart. For example, preferred and alternative embodiments are disclosedherein.

Additionally, like numbers refer to identical, like, or similar elementsthroughout, although such numbers may be referenced in the context ofdifferent embodiments. As used herein, the term “and/or” includes anyand all combinations of one or more of the associated listed items.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

On our globe today, there are regions on the earth where people havewater sources, but no means of purifying it before consumption.Moreover, infrastructure in these areas limit the use of electricpowered purifying methods leaving them to drink unclean water. It istherefore deemed necessary to ensure the unit produced be aselectrically independent as possible, and with a low manufacturing andimplementation cost. Therefore, it is considered a vital part of thedisclosed embodiments and any variations thereof to maintain low costsfor it to be considered a viable solution.

FIG. 2 illustrates a three-dimensional view of a solar still 20, whichcan be implemented in accordance with a preferred embodiment. As will bediscussed in greater detail herein, a variety of embodiments can beimplemented, which vary in scope from one another, but which achieve theviable solution referred to above. In some example embodiments, twostages configured in series, known as “effects,” can be implemented. Thefirst effect absorbs energy during the day and utilizes a heat exchangerfor the condensing process. The energy gained from the heat exchangercan then be transferred to the second effect as a heat source to produceevaporation for condensate during night hours. Water in the second unitloses heat during night time so the cooled water from the second unitcan be utilized again in the heat exchanger during the day time toproduce condensate, and the cycle can then repeat. This dual effect unithas shown significant advances over the standard still and yet haspotential room for even greater improvements.

In the configuration shown in FIG. 2, the system or solar still 20includes a solar collector 22 with respect to a condenser 24. A secondeffect 28 is also depicted in FIG. 2 (i.e., the pyramid-shaped structureshown in FIG. 2). Insulated components 26 and 29 are also illustrated inin FIG. 2.

The disclosed embodiments can be implemented in, for example, threephases as follows: (i) data acquisition deployment; (ii) preliminaryanalysis and optimization; and (iii) design improvements.

Regarding data acquisition deployment, a data acquisition (DAQ) systemcan be implemented using, for example, National Instruments LabVIEW toautomatically record the thermodynamic performance of a solar still suchas the solar still or system 20 shown in FIG. 2. For analysis of thethermodynamic efficiency of the still, a pyranometer can be used tomeasure the cumulative solar energy. In addition, thermocouples andhumidity sensors can be installed at strategic locations, and a liquidflow meter was installed to monitor the chill flow with respect to, forexample, the condenser 24 depicted in FIG. 2. Data from such sensors canenable calculations of enthalpy throughout the distiller. It should benoted that an analysis of the unit's ability to remove salinity is alsoimportant, and this can be accomplished by measuring the conductivity ofthe raw water and distilled water. A GUI (Graphical User Interface) suchas a VI (Virtual Interface) can be utilized to provide a user-friendlyinterface with real time signal measurements which the user caninitiate, observe all sensors, save, and shutdown the program. Ascreen-capture of an example VI interface is depicted is shown in FIG.3. That is, FIG. 3 illustrates a sample image of a GUI (Graphical UserInterface) 30, in accordance with an example embodiment.

FIG. 4 illustrates a schematic diagram of a system 40 composed of anarrangement of thermocouples, humidity sensors, and conductivity cells,in accordance with an example embodiment. The solar still or solar stillsystem 40 shown in FIG. 4 includes a 1st effect solar collector 25 thatproduces evaporated water with respect to a condenser 24. A water source32 supplies water to the first effect 25. A second effect 28 is alsoshown in FIG. 4 with respect to the condenser 24, and the 1st effectsolar collector 25. FIG. 4 further illustrates the resulting clean water34 produced.

Regarding sensor placement, a pyranometer, one or more thermocouples,one or more humidity sensors, and one or more conductivity cells can beinstalled throughout the solar still and/or the solar still system 40.In an experimental embodiment, for example, a pyranometer depicted via asun symbol can be located twenty feet away from the solar still to avoidshadows. Six thermocouples can be placed inside the solar collector ofthe first effect 25 to observe spatial variability in moist-air flow.Another thermocouple can be placed away from the system to measureambient temperatures. An additional six thermocouples can be installedin the condenser to observe spatial variation in air movement. Theremaining two thermocouples can be located within the second effect 28to measure the temperature of the liquid and the internal ambientenvironment of the effect. Three relative humidity sensors can belocated within the prototype: the solar collector of the first effect25, the condenser of the first effect 25, and in the second effect 28.Three conductivity sensors can be located in: (1) the source water 32,(2) first effect distillate water, and (3) the second effect 28.

The following are example data acquisition devices and sensors that canbe implemented in the context of the experimental embodiment describedabove:

-   -   Qty-1 National Instruments eDAQ-9172 Compact DAQ Chassis: this        component supports up to eight C Series I/O modules which, in        conjunction with the modules, aid in data acquisition and        provide power to support modules as well as common reference        grounds.    -   Qty-1 National Instruments NI 9203 DAQ Module: this component is        a support module for the chassis described above which possesses        an 8-channel ±20 mA input which supports various sensors.    -   Qty-1 Micronta 12V Regulated Power Supply: provides power to all        various sensors and modules.    -   Qty-1 Apogee SP-214 amplified 4-20 mA pyranometer: this        instrument measures the total solar shortwave radiation in W        m⁻².    -   Qty-1 National Instruments NI 9211A DAQ thermocouple module:        this component is designed especially for 16 thermocouples.    -   Qty-100 ft K-Type thermocouple wire: these components measure        the temperature in the ambient and internal environments of the        prototype unit; the wire was cut into 16 individual thermocouple        sensors.    -   Qty-3 George Fischer Conductivity Sensors with accompanying        support Universal J Boxes: these components perform conductivity        measurements ranging from 0-200,000 μS/cm.    -   Qty-3 Omega HX92 AC-RP1 humidity sensors with probes: these        sensors provide relative humidity data within the ambient and        internal environments of the prototype unit.    -   Qty-1 Omega HHF11A handheld air flow meter: provides air flow        measurements in various areas on the prototype unit.    -   Qty-1 Omega FLR1011-D water flow meter: provides liquid flow        rate data logging for the condenser inlet.

It can be appreciated that the various components and sensing devicesdescribed above are presented herein for illustrative purposes only anddo not constitute limiting features of the disclosed embodiments.

Testing the solar still involved two test cycles, a day cycle and anight cycle. The day cycle testing was performed with mostly clear skiesin order to record and analyze the still's performance under goodconditions. Tests were performed at the Kay Bailey Hutchisondesalination plant in El Paso, Tex. Untreated brackish water(approximately 2500 mg/L) was used as the source water. (As these testslasted a maximum of 36 hours, the effects of mineral scaling were notobserved in the first or second effects.)

For the day cycle, a tank filled with brackish water was used as thesource feed for the first effect floor circulation and condenser chillfluid. Flow rates through the condenser were limited to a maximum of0.81 mL/min due to the storage capacity of the insulated reservoirs. Thesolar collector of the first effect regularly adjusted constantly tomaintain an orthogonal relationship to the sun at all times. The base ofthe still can rotate and the unit can incline up to 75 degrees fromhorizontal. Lastly, the LabVIEW program was set to record data at oneminute intervals.

For the night cycle, a pump is used to feed the hot water from the daycycle (stored in the insulated reservoirs) into the second effect andback into the insulated reservoirs. At the end of the night cycle, theremaining, unevaporated water was recycled for the following daytimecycle.

While testing the prototype on a cold morning, the team visuallyobserved random movement of water vapor in the solar collector. The teamrealized that the prototype was designed to rely on natural convectioninside the solar still to transport humid air to the condenser above,but it seemed to be limited by random, chaotic air movements. Also, coldair inside the condenser descends, preventing the evaporated water fromreaching the condenser, and in some cases, simply producing horizontalswirling motion inside the solar collector.

In order to solve this problem, a four-inch PVC return duct wasdeveloped to return cold air coming out of the top of the condenser tothe base of the solar collector. The design of the cold air return ductprovided natural (buoyancy-driven) convection through the first effectto provide consistent and smooth air flow. This improvement resulted inmore uniform and consistent temperature performance in the solarcollector and the condenser, but most importantly, heat transfer throughthe wall of the duct allowed water to condense inside the duct.Implementation of this duct improved the water production of the systemby 20-30%. It was calculated that the amount of heat loss throughout theduct was around 50 W. FIG. 5 illustrates a pictorial diagram of thecold-air return duct 50 described above, which can be implemented inaccordance with an example embodiment.

To study the effects of cold-air return duct, tests were performed inthree stages: (1) original, no cold air recirculation duct; (2) natural(buoyancy-driven) convection with a cold air return duct; and (3) andfan-forced convection through the return duct. A list of a comparison oftotal system distillate production is shown in graph 60 in FIG. 6 as afunction of air velocity in the return duct. Natural convection produceda duct air speed of approximately 1 m/s, and in one test, air flow wasrestricted to 0.1 m/s. A fan was used inside the duct to force an airspeed of approximately 5 m/s.

TABLE 1 Summary of experiments with modified air-recirculation ReturnDuct Total Solar Daytime Night time Total Air Velocity RadiationDistillate Distillate Production Date of Run Configuration (m/s) (W/m²)(L) (L) (L) April 4^(th) Original KII 0 6.2 2.5 — — configuration April6^(th) Natural 1 6.7 4.3 — — convection April 11^(th) Original KII 0 7.65.4 3.0 8.4 configuration April 19^(th) Natural 1 8.1 8.2 3.0 11.2convection April 26^(th) Fan-forced 5 7.5 8.0 3.0 11.0 convection April27^(th) Throttled 0.1 8.0 7.2 — — convection May 29^(th) Natural 1 7.96.7 — — convection

Overall, the system operating with natural convection produced themaximum total distillate in a 24 hour cycle, which was an improvementapproximately 30% compared to the original configuration of theprototype still.

To compare the overall efficiencies, the overall efficiency is takenfrom two 24 hour data cycles. One data cycle consists of its originalsetup and the other data cycle is with improvements implemented byHydro5. The first data is from April 11 (Day 1) which was in itsoriginal setup. On this day, the first effect was run for a total of10.75 hr, collected an estimated 10.62 kWh, produced a total of 5.4 L ofdistillate, and the condenser removed a total of 4.27 kWh. Theefficiency of the first effect system in its original configuration isη=4.27/10.62=40%.

The second set of data is from April 19 with the addition of a cold airreturn duct. On this day, the first effect was operated for a total of11.5 hrs, collected an estimated 11.3 kWh, produced a total of 8.15liters of distillate, and the condenser removed a total of 8.98 kWh.With the addition of the duct, this brought the efficiency of the systemto η=8.98/11.3=80%. Based on these data, the implementation of the ductdoubled the efficiency of the system.

The solar collector area is 1.4 m is the area on the first effect thatcollects solar energy. (Note that the energy input from the pump isomitted from the overall system efficiency calculation due to the factthat the pump provided by Suns River/KII Inc. can be substituted by alower power pumps.)

Regarding the efficiency of latent heat recovery, first, the efficiencywas calculated from data collected on April 11 which was in its originalconfiguration. The efficiency for the total solar still system includingfirst and second effect was 52.5%. The second efficiency was calculatedon April 19 with the implementation of the cold air return duct and wascalculated at 64.6%. This was an improvement of 23% on the entire solardistiller system. This calculation was done by multiplying the totalmass of distillate water produced by the entire system by the heat ofvaporization of water by the total amount of solar energy.

In order to improve the distribution of air from the return air duct atthe base of the solar collector, two air vents were designed to beplaced at the end of the duct. The design was made using SolidWorkssoftware and printing them out at the UTEP Mechanical EngineeringMachine Shop with rapid prototyping 3-D printing. The vent foils aredesigned to be at an angle to allow a better distribution throughout thesolar collector. FIG. 7 illustrates one example of a solar collector airvent 70, which can be implemented in accordance with an alternativeembodiment.

In order to increase efficiency and productivity produced by the 2ndeffect pyramid, we implemented a black cloth to the bottom of it, so itcan behave as a black body itself. By doing so the pyramid can collectmore solar energy, which translates into higher temperature, humidity,and higher water production by this element alone. The amount ofdistillate produced before this improvement was 1 liter during the daycycle and three liters during the night cycle. With the black bodyfloor, we were able to produce 1.5 liters during the day cycle. This isa 50% increase for the day cycle. The night cycle didn't get affected bythis improvement, in both occasions we were able to produce 3 litersduring the night.

The solar collector of the first unit is insulated utilizing a doublepane glass. Solar energy passes through the glass and serves as aninsulator to keep heat in. Currently the air gap is approximately 5 cm.Resistance modeling was used to calculate the heat loss through thedouble pane system, as shown in graph 80 of FIG. 8. The optimal air gapdepends on how well the sides are insulated and how much material wouldbe available to provide an air gap. This figure should serve as guidefor further research to avoid losing energy through the solar collector.

FIG. 9 illustrates an image of an evaporator glass 150, which may beimplemented in accordance with an example embodiment. FIG. 10illustrates an image of a condenser coil 160, which can be implementedin accordance with an example embodiment

FIGS. 11A-11B illustrate graphs indicative of sample day-cycleperformance (April 4), in accordance with an example embodiment. FIGS.12A-12B illustrate graphs indicative of sample day-cycle performance(April 6), in accordance with an example embodiment. FIGS. 13A-13Billustrate graphs indicative of sample day-cycle performance (April 11),in accordance with an example embodiment. FIGS. 14A-14B illustrategraphs indicative of sample day-cycle performance (April 19), inaccordance with an example embodiment. FIGS. 15A-15B illustrate graphsindicative of sample day-cycle performance (April 26), in accordancewith an example embodiment. FIGS. 16A-16B illustrates graphs indicativeof sample day-cycle performance (April 27), in accordance with anexample embodiment.

The disclosed embodiments are particularly suited to producing fresh orpotable water from sea water and other salty waters, such as those indesert and semi-desert areas, as examples. Such embodiments andvariations thereof are applicable in many other areas as well. Thedisclosed embodiments can be implemented to provide large quantities ofwater from salty water to supply irrigation, industrial, and municipalwater by using inexpensive material already widely available at lowcosts throughout the world with minimal energy required and simpleoperation and upkeep.

As indicated earlier, attempts have been made in the past to providesolar stills capable of producing relatively large quantities of potablewater. These attempts have proven to be costly and inefficient and havefailed at producing large quantities of potable water. Otherdesalination technology is complex, energy intensive, and delivers onlylow yield from feed water. Therefore, a need exists for an improvedsolar collection system combined with thermal distillation.

One objective of the disclosed embodiments is utilization of theabundance of solar energy to address water demands in desert andsemi-desert regions. Another objective is to meld solar energycollection and thermal distillation processes to produce high qualitywater in quantity for domestic, community, and industrial needs.

In an example embodiment, a process for desalination can be implemented,which utilizes a solar still. Such a solar still can be configured toinclude a first end and an opposite second end, with the longitudinalaxis extending between the ends, and a raised side and an oppositelowered side, with the width axis extending between the sides. The solarstill can further include a heating surface being inclined along adirection aligned with or parallel to a width so that the water flowsdown the heating surface along or parallel with the width axis. Thesolar still also includes at least one solar-transmitting roof top toadmit solar energy to the equipment. The solar still includes at leastone tubular member extending below the heating surface between thesides. The solar still includes at least one collection troughpositioned to receive condensed water dripping from the tubular member.

The solar still may also include a liquid distributor positioned alongthe raised side of the heating surface to distribute water dischargedfrom the distributor substantially across the length of the heatingsurface so that the water flows down the heating surface along orparallel with the width axis. Some non-limiting examples of solar stillsare described in U.S. Pat. No. 8,088,257, issued Jan. 3, 2012, U.S. Pat.No. 8,580,085 issued Nov. 12, 2013, and Australian Patent 2008317021issued Aug. 9, 2012, the disclosures of which are respectivelyincorporated herein by reference in their entirety. Note that suchexamples are not considered limiting features of the disclosedembodiments, but are mentioned for illustrative and exemplary purposesonly.

FIG. 17 illustrates a block diagram of a solar powered thermaldistillation system 200, which may be implemented in accordance with anexample embodiment. The configuration shown in FIG. 17 is presentedherein to illustrate the general principals of an example solar poweredthermal distillation system. The system 200 depicted in FIG. 17 includesa solar still 204 (similar to the previously discussed solar stills)having a first end and an opposite second end with a longitudinal accessextending between the first end and the opposite second end, the solarstill further having a raised side and an opposite lowered side with awidth axis extending between the raised side and the opposite loweredside (as discussed previously). The system 200 further includes asolar-transmitting roof 208, which can be located atop the solar still204, such that the solar-transmitting roof 208 admits solar energy toelectrical and/or electromechanical equipment 206 maintained within thesolar still 204. The solar still 204 can be configured to furtherinclude a heating surface 202 that is inclined along a direction alignedwith or parallel to the width axis so that water flows down the heatingsurface 202 along or parallel with the width axis (as also discussedpreviously). The solar still 204 can be configured to further include atubular member 210 that extends below the heating surface 202 betweenthe aforementioned raised side and the opposite lowered side. The solarstill 204 additionally can be configured to include one or morecollection trough(s) 212 positioned to receive condensed water drippingfrom the tubular member 210.

Note that in one example embodiment, energy recovered in the solar stillin the form of heated water may be delivered to a vessel that isoperated under vacuum. The vacuum vessel may include one or moreelongated tubular member and a trough to collect condensate drippingfrom the tubular member. Additionally, in some example embodiments, thevacuum vessel may optimally be enclosed in another vessel whichenclosing vessel may also be maintained under vacuum conditions. Waterfrom the interior vessel which does not flash may be transferred toanother vessel operated at a greater vacuum for further flashing. Theflows from one stage to the next may be regulated by use of variousmeasurement and control devices used to stabilize operations andoptimize performance.

One pair of internal and external containment vessels with tubularmember and trough to recover condensed water constitutes onestage/effect and multiple stages/effects, each with greater vacuum ortemperature, can be combined to produce additional pure water at each ofthe multiple stages/effects. Water heated in the multiple stages/effectscan be used to condense flashed water vapor in the earlier, hotterstages and routed through the solar still to the first stage.Additionally, cold water heated in the tubular member of some stages canbe stored in vessel which has a transparent canopy with sloped roof. Thecanopy can include troughs to collect purified water which may form onthe interior sloped roof of the canopy and drip into the troughs. Theunevaporated water in the vessel under the canopy may optimally becooled sufficiently to be used as cold water in one or more of themultiple stage flash tubular members.

In some example embodiments, other sources of low temperature energy canbe used to add thermal energy to the system. These sources might includelow pressure steam, hot boiler blowdown, hot process streams, or othersources incident to the equipment.

In other example embodiments, the system vacuum may be maintained by theuse of a direct condensation of the vapor from the final stage in anelevated tank using cold water to condense the vapor. The system vacuummay be maintained using various mechanical devices, educators, or otherdevices designed to create vacuum.

The disclosed solar distillation system is especially suited toproducing fresh or potable water from sea water in west coast deserts inthe rain shadow created by cold ocean currents offshore (e.g., theSahara, Namibia, Australia, et al.). The disclosed embodiments areapplicable in many other areas as well. The disclosed embodiments may beimplemented, for example, to provide large quantities of water fromsalty water to supply irrigation, industrial, and municipal water byusing inexpensive material already widely available at low coststhroughout the world with minimal energy required and simple operationand upkeep.

It will be appreciated that variations of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. It will alsobe appreciated various presently unforeseen or unanticipatedalternatives, modifications, variations or improvements therein may besubsequently made by those skilled in the art, which are also intendedto be encompassed by the following claims.

What is claimed is:
 1. A solar powered thermal distillation system,comprising: a solar still having a first end and an opposite second endwith a longitudinal access extending between said first end and saidopposite second end, said solar still further having a raised side andan opposite lowered side with a width axis extending between said raisedside and said opposite lowered side; at least one solar-transmittingroof atop said solar still, wherein said at least one solar-transmittingroof admits solar energy to electrical and/or electromechanicalequipment maintained within said solar still; said solar still furthercomprising a heating surface inclined along a direction aligned with orparallel to said width axis so that water flows down said heatingsurface along or parallel with said width axis; said solar stillincluding a tubular member extending below said heating surface betweensaid raised side and said opposite lowered side; and said solar stillhaving at least one collection trough positioned to receive condensedwater dripping from said tubular member.
 2. The system of claim 1wherein said solar still further comprises a liquid distributorpositioned along said raised side of said heating surface to distributewater discharged from said liquid distributor substantially across alength of heating.
 3. The system of claim 1 wherein energy recovered insaid solar still in a form of heated water is delivered to a vesseloperated under a vacuum.
 4. The system of claim 3 wherein said vesselincludes said tubular member and said at least one collection trough tocollect condensate dripping from said at least one tubular member. 5.The system of claim 3 wherein said vessel is enclosed within an exteriorvessel that is also maintained under a vacuum condition such that saidvessel comprises an interior vessel maintained within said exteriorvessel.
 6. The system of claim 5 wherein water that does not flash istransferred to another vessel operated at a greater vacuum for furtherflashing.
 7. The system of claim 5 wherein said interior and exteriorvessels comprise a pair of internal and external containment vessels inassociation with said tubular member and said at least one collectiontrough to recover condensed water, wherein said pair of internal andexternal containment vessels constitute a one stage/effect and multiplestages/effects, each with greater vacuum or temperature, which arecombinable to produce pure water at each of said multiplestages/effects.
 8. The system of claim 7 wherein water heated in saidmultiple stages/effects is used to condense flashed water vapor inearlier and hotter stages and routed through said solar still to a firststage.
 9. The system of claim 7 wherein cold water heated in saidtubular member is storable in said vessel, wherein said vessel includesa transparent canopy with sloped roof.
 10. The system of claim 9 whereinsaid transparent canopy comprises a plurality of troughs for collectingpurified water.
 11. A solar powered thermal distillation system,comprising: a solar still having a first end and an opposite second endwith a longitudinal access extending between said first end and saidopposite second end, said solar still further having a raised side andan opposite lowered side with a width axis extending between said raisedside and said opposite lowered side; at least one solar-transmittingroof atop said solar still, wherein said at least one solar-transmittingroof admits solar energy to electrical and/or electromechanicalequipment maintained within said solar still; and said solar stillfurther comprising a heating surface inclined along a direction alignedwith or parallel to said width axis so that water flows down saidheating surface along or parallel with said width axis.
 12. The systemof claim 11 wherein: said solar still further comprises a tubular memberextending below said heating surface between said raised side and saidopposite lowered side; and said solar still comprises at least onecollection trough positioned to receive condensed water dripping fromsaid tubular member.
 13. The system of claim 11 wherein said solar stillfurther comprises a liquid distributor positioned along said raised sideof said heating surface to distribute water discharged from said liquiddistributor substantially across a length of heating.
 14. The system ofclaim 12 wherein energy recovered in said solar still in a form ofheated water is delivered to a vessel operated under a vacuum andwherein said vessel includes said tubular member and said at least onecollection trough to collect condensate dripping from said at least onetubular member.
 15. The system of claim 12 wherein said vessel isenclosed within an exterior vessel that is also maintained under avacuum condition such that said vessel comprises an interior vesselmaintained within said exterior vessel and wherein water that does notflash is transferred to another vessel operated at a greater vacuum forfurther flashing.
 16. A method of configuring a solar still for solarpowered thermal distillation, said method comprising: configuring asolar still with a first end and an opposite second end with alongitudinal access extending between said first end and said oppositesecond end, said solar still further having a raised side and anopposite lowered side with a width axis extending between said raisedside and said opposite lowered side; providing at least onesolar-transmitting roof atop said solar still, wherein said at least onesolar-transmitting roof admits solar energy to electrical and/orelectromechanical equipment maintained within said solar still;configuring solar still with a heating surface inclined along adirection aligned with or parallel to said width axis so that waterflows down said heating surface along or parallel with said width axis;modifying said solar still to include a tubular member extending belowsaid heating surface between said raised side and said opposite loweredside; and providing said solar still with at least one collection troughpositioned to receive condensed water dripping from said tubular member.17. The method of claim 16 further comprising configuring said solarstill with a liquid distributor positioned along said raised side ofsaid heating surface to distribute water discharged from said liquiddistributor substantially across a length of heating, wherein energyrecovered in said solar still in a form of heated water is delivered toa vessel operated under a vacuum.
 18. The method of claim 17 whereinsaid vessel includes said tubular member and said at least onecollection trough to collect condensate dripping from said at least onetubular member.
 19. The method of claim 17 wherein said vessel isenclosed within an exterior vessel that is also maintained under avacuum condition such that said vessel comprises an interior vesselmaintained within said exterior vessel.
 20. The method of claim 5further comprising configuring said interior and exterior vessels toinclude a pair of internal and external containment vessels inassociation with said tubular member and said at least one collectiontrough to recover condensed water, wherein said pair of internal andexternal containment vessels constitute a one stage/effect and multiplestages/effects, each with greater vacuum or temperature, which arecombinable to produce pure water at each of said multiplestages/effects.